In a vehicle air conditioner described in U.S. Pat. No. 6,431,257 (corresponding to JP-A-2001-105830), a heating heat exchanger, a cool air bypass passage and an air mixing door are suitably arranged with respect to a cooling heat exchanger constructed of an evaporator of a refrigerant cycle, so that a size of an interior air-conditioning unit is reduced. However, in this vehicle air conditioner, a maximum cooling capacity to be necessary is obtained only using the single cooling heat exchanger. Accordingly, the size of the cooling heat exchanger necessarily becomes larger when, the maximum cooling capacity is set larger. Therefore, it is difficult to reduce the size of the interior air-conditioning unit.
Furthermore, in a vehicle air conditioner described in U.S. Pat. No. 6,449,974 (corresponding to JP-A-2002-46448), an auxiliary heat exchanger is arranged at a downstream air side of a cooling heat exchanger constructed of an evaporator of a refrigerant cycle. The auxiliary heat exchanger is capable of switching between a heating function and a cooling function. In addition, a heating heat exchanger in which hot water (engine-cooling water) flows is arranged at a downstream air side of the auxiliary heat exchanger.
In this vehicle air conditioner described in U.S. Pat. No. 6,449,974, when a maximum cooling operation is set, the auxiliary heat exchanger is arranged in series with the cooling heat exchanger in a low-pressure side of the refrigerant cycle so that both the cooling heat exchanger and the auxiliary heat exchanger are used as evaporators. However, in this case, because the three heat exchangers are used in the interior air-conditioning unit, arrangement spaces of the three heat exchangers becomes large, and thereby increasing the size of the interior air-conditioning unit.